1. Field of the Invention
The present invention relates generally to resource discovery in wireless communication, and more particularly, to a method and an apparatus for signal design for efficiently indicating discovery of signal resources to a device in wireless communication.
2. Description of the Related Art
The 3rd Generation Partnership Project (3GPP), which is the standards group for asynchronous cellular mobile communication, has studied Device-to-Device (D2D) communication between devices using Long Term Evolution (LTE) system standards, as well as the conventional wireless communication between a base station and a User Equipment (UE). An important requirement for D2D communication is to enable D2D communication, not only in a situation capable of receiving a conventional cellular system service, but also in a situation incapable of receiving the cellular system service. For example, in a situation in which a base station cannot operate, i.e., cannot provide a cellular service, due to, for example, a natural disaster, an emergency communication between users through D2D communication is required.
A D2D communication process inevitably includes a discovery operation in which one UE discovers surrounding UEs. To this end, each UE supporting D2D transmits a discovery signal to surrounding UEs to enable the surrounding UEs to recognize its existence. The UE then receives discovery signals transmitted from the surrounding UEs to recognize the existence of the surrounding UEs.
Each UE can efficiently perform discovery signal transmission and reception only when it has acquired an identical time reference, i.e., commonly applicable time synchronization, and when it knows configuration information relating to discovery signal transmission/reception resources. For example, when synchronization between UEs is acquired, UEs performing D2D communication may transmit or receive a discovery signal only at a particular time resource based on a common time to minimize the electric power consumption for monitoring of a discovery signal from another UE.
If synchronization between UEs is not acquired, respective UEs transmit their own discovery signals at different time points. The respective UEs should always monitor discovery signals from other UEs in order to receive the discovery signals, which increases the power consumption of each UE.
As described above, a discovery process is an indispensable operation in D2D communication, and synchronization between UEs should be established in order to efficiently perform the discovery process. In general, UEs can establish synchronization by acquiring a common time reference from a base station or a network. However, in an emergency situation, if a base station or network is unable to provide a cellular service, there is no other device available for acquiring synchronization between UEs.
In order to solve this problem, a method has been studied of providing a D2D synchronization signal to UEs within an area unable to provide cellular service, by a UE currently belonging to a normal base station adjacent to the area. However, not only the D2D synchronization signal, but also discovery signal resource configuration information should be shared between UEs in the area unable to provide cellular service in order to achieve a smooth discovery operation. To this end, use of an additional D2D communication resource to transmit discovery signal configuration information by a UE belonging to a normal base station is not preferable in view of resource consumption and an increase of limitation in use of existing cellular UE communication resources.